Upgrade it all to hosting.

You can get 5x the hashing power for the same money, and none of the electricity or hassle.

I was very happy when I saw the option to transfer my order of a 25 GH Little single to 125 GH hosting.

Yes, difficulty will be up more by january/february, but the growth will be linear from now on -- and it's not mathematically possible to be going up 40% exponentially forever.